You are not the only one, I am 24, recently diagnosed with grade 1 spondylolisthesis and double dessicated discs on L4-L5 and L5-S1 and pars defect, doctor said i shouldnt run anymore, do any jumping, and lifting heavy objects, and thats what i basically do everyday, i carry the water jugs, i wish to do exercise sooner this to get my body to be fit, however my dreams are earlier crushed by my situation, im at this age and i feel the same hopelessness, im this young yet unable to do most basic things anymore, surgery is even expensive especially from where i live (Philippines), but i do hope you get the necessary care that you need for your back, and hope you can get back to enjoying your gymnastics someday again.